测定室内空气中菌落总数时，采样器采样前，应对采样系统气密性进行检查，不得漏气。
参考答案：对
海豚、海豹、鲸、海狮等是生活在海洋中的哺乳动物，它们用______呼吸．
A distribution with a mean of 15 and a range of 2 to 25 would be:（）
A. normally distributed.
B. positively skewed to the right.
C. cannot be determine.
